As a result of their increased performance in terms of output and specific power and power density, synchronous machines with permanent magnets nowadays have an extensive application in the field of motor vehicles.
These electrical machines can be produced in a wide range of powers and speeds, and have applications both in vehicles of the all-electric type and in vehicles with low CO2 emission, of the types known as mild-hybrid and full-hybrid.
The mild-hybrid applications generally relate to electrical machines of approximately 8 to 10 kW, for example an electric motor fitted on the front face of a thermal engine, and coupled to the latter by a drive belt. By means of an electric motor of this type, it is possible to reduce the capacity of the thermal motorisation (engine downsizing) by providing electric torque assistance which supplies additional power, in particular when restarting. In addition, traction at low speed, for example in an urban environment, can also be ensured by this same electric motor.
Applications of the full-hybrid type generally relate to 25 to 50 kW motors for architectures of the series and/or parallel type, with more refined integration of the electric motor(s) in the traction chain of the vehicle, in particular at the level of the clutch.
The remarkable performance levels of the present machines with permanent magnets are to a large extent due to rotors which have a so-called “flux concentration” structure which makes it possible to obtain substantial magnetic fluxes with magnets obtained from sintered or bonded ferrites.
In these machines, the stator surrounds the rotor, and its magnetic mass has a series of notches, generally parallel to the axis of rotation, delimiting teeth around which there are formed windings which create the rotary magnetic fields that drive the rotor.
The control of an inverter which supplies the stator windings from on-board direct current supply sources requires knowledge of the angular position of the rotor relative to the stator, as well as of the speed of rotation and other parameters.
For this purpose, certain electrical machines which are used in the motor vehicle industry are equipped with a device known as a “resolver” arranged at the end of the rotor shaft.
A resolver of this type itself comprises a rotor and a stator which are fixed respectively relative to the rotor and the stator of the machine.
However, this type of equipment has disadvantages, in particular its cost, and the company VALEO EQUIPMENTS ELECTRIQUES MOTEUR has proposed in patent application FR2872644 another device for determination of the angular position of the rotor.
The device described does not involve any costly equipment, since the magnetic field is supplied directly, either by the rotor of the machine itself, or by a magnetic target secured on the shaft.
Means for processing first signals emitted by Hall-effect sensors provide second signals which are representative of the angular position of the rotor and of the speed of rotation, and other information which is useful for the functioning of the inverter.
However, when implementing this device, the inventive body found that it was relatively difficult to process the first signals in order to obtain satisfactory precision relating to the angular position of the rotor in all cases, and to eliminate the parasitic influences completely.